The metabolism of glycogen in human skin fibroblasts grown in tissue culture will be studied from the point of view of finding what proportion of total glycogen catabolism goes by a mechanism involving lysosomal uptake and intralysosomal hydrolytic degradation. Normal cell lines grown from the skin of patients with various types of glycogen storage diseases will be used. Particular attention will be focused on cells from individuals with the "infantile" and others with the "adult" form of Type II glycogen disease (acid alpha-glucosidase deficiency), as well as other cells from patients with Type IV glycogen storage disease (branching enzyme deficiency). Rates of glycogen synthesis and of glycogen degradation will be measured in these cells, in normal control cells, and in cells of other mutant types. The nature of the residual branching activity, if there is any, in the Type IV cell will be investigated both as to kinetic properties and substrate specificity.